A gear-operated speed change apparatus for an automatic transmission, which is constructed to include an input shaft, one set of double-pinion type planetary gear, a composite planetary gear train (as will be referred as the “Ravigneaux type composite planetary gear train”) having a sun gear meshing individually with double pinions, four clutches, two brakes and an output shaft and which is enabled to achieve gear ranges of seven forward speeds and one reverse speed or more by engaging/releasing the four clutches and the two brakes properly as speed-changing elements, has been hitherto proposed as described in FIG. 2 and Table 2 (eight forward speeds and two reverse speeds) of JP-A-2001-182785.
However, the gear-operated speed change apparatus adopting this Ravigneaux type composite planetary gear train has the problems, as enumerated in the following.    {circle around (1)} The strength is at a disadvantage because the maximum torque (for a 1st speed) of the gear train is borne by the double-pinion type planetary gear on one side of the Ravigneaux type composite planetary gear train.    {circle around (2)} Another disadvantage resides in the gear strength, the gear lifetime or the carrier rigidity, because the torque augmented by one double-pinion type planetary gear acting as a speed-reducing device is inputted at 1st to 4th speeds from the sun gear of the Ravigneaux type composite planetary gear train so that the tangential force becomes higher than that of a ring gear input.    {circle around (3)} The Ravigneaux type composite planetary gear train has to be enlarged to enlarge the automatic transmission, because there are demanded both the securement of the strength (e.g., the gear strength or the gear lifetime) of the Ravigneaux type composite planetary gear train at the 1st speed and the improvement in the gear strength, the gear lifetime or the carrier rigidity of the Ravigneaux type composite planetary gear train.    {circle around (4)} At the 2nd speed, a torque circulation occurs in the Ravigneaux type composite planetary gear train so that the transmission efficiency drops to deteriorate the fuel economy at the 2nd speed where the torque circulation occurs.
The present invention has been conceived noting the above-specified problems and has an object to provide a gear-operated speed change apparatus for an automatic transmission, which can make the degree of freedom for selecting a gear ratio higher than that of the case using the Ravigneaux type composite planetary gear train, while achieving a strength advantage of the gear train, an improvement in the fuel economy, the coaxial positioning of the input portion and the output portion and the size reduction of the automatic transmission altogether.